Methods of forming variable resistance memory cells, and methods of etching germanium, antimony, and tellurium-comprising materials

ABSTRACT

A method of etching a material that includes comprising germanium, antimony, and tellurium encompasses exposing said material to a plasma-enhanced etching chemistry comprising Cl 2  and CH 2 F 2 . A method of forming a variable resistance memory cell includes forming a conductive inner electrode material over a substrate. A variable resistance chalcogenide material comprising germanium, antimony, and tellurium is formed over the conductive inner electrode material. A conductive outer electrode material is formed over the chalcogenide material. The germanium, antimony, and tellurium-comprising material is plasma etched using a chemistry comprising Cl 2  and CH 2 F 2 .

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 11/450,020 which was filed Jun. 9, 2006 that isincorporated by reference herein.

TECHNICAL FIELD

This invention relates to methods of forming variable resistance memorycells, and to methods of etching materials comprising germanium,antimony, and tellurium.

BACKGROUND OF THE INVENTION

Semiconductor fabrication continues to strive to make individualelectronic components smaller and smaller, resulting in ever denserintegrated circuitry. One type of integrated circuitry comprises memorycircuitry where information is stored in the form of binary data. Memorycircuitry can be characterized by whether the data is volatile ornon-volatile. Generally, volatile memory circuitry loses stored datawhen power is interrupted, while non-volatile memory circuitry retainsstored data even during power interruption.

Some non-volatile memory devices utilize a material whose resistance canbe controllably modified into two or more states of differentresistance, thus enabling the devices to comprise settable memory.Exemplary particular types of memory device which utilizes suchresistance variable material are programmable conductive random accessmemory and phase change random access memory. Phase change random accessmemory comprises a fast ion conductor or resistance variable material,typically a chalcogenide material having metal ions therein, which isdisposed between two conductive electrodes. By way of example only, suchare disclosed in U.S. Pat. Nos. 5,761,115; 5,896,312; 5,914,893 and6,084,796 to Kozicki et al. Resistance variable materials are capable ofassuming high resistance “off” and low resistance “on” states inresponse to a stimulus for a binary memory, and multiple generallystable states in response to a stimulus for a higher order memory. Theresultant memory element is non-volatile in that it will maintain theintegrity of the information stored by the memory cell without the needfor periodic refresh signals, and the data integrity of the informationstored by these memory cells is not lost when power is removed from thedevice.

As new variable resistance chalcogenide materials for memory devices aredeveloped, new techniques need to be developed to be able to patternsuch materials into desired shapes and configurations for memory cells.

While the invention was motivated in addressing the above identifiedissues, it is in no way so limited. The invention is only limited by theaccompanying claims as literally worded, without interpretative or otherlimiting reference to the specification, and in accordance with thedoctrine of equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic section of a substrate fragment in process inaccordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a diagrammatic section of another substrate fragment inprocess in accordance with an aspect of the invention.

FIG. 4 is a view of the FIG. 3 substrate fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a diagrammatic section of still another substrate fragment inprocess in accordance with an aspect of the invention.

FIG. 6 is a view of the FIG. 5 substrate fragment at a processing stepsubsequent to that shown by FIG. 5.

FIG. 7 is a view of the FIG. 6 substrate fragment at a processing stepsubsequent to that shown by FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Aspects of the invention encompass methods of forming a memory cellwhich include plasma etching of a variable resistance chalcogenidematerial comprising germanium, antimony, and tellurium. Aspects of theinvention also encompass methods of etching a material comprisinggermanium, antimony, and tellurium independent of the purpose orconstruction for which such material is fabricated.

A first exemplary implementation is described with reference to FIGS. 1and 2. FIG. 1 depicts a substrate fragment indicated generally withreference numeral 10. In one preferred implementation, such comprises asemiconductor substrate 12 having a material 14 comprising germanium,antimony, and tellurium received thereover. Substrate 12 might comprisea semiconductor or other substrate. If a semiconductor substrate, suchmight comprise doped and/or undoped semiconductive materials incombination with one or more other materials, layers, and/or regions.Such might comprise semiconductor-on-insulator substrates and/or othersubstrates. In the context of this document, the term “semiconductorsubstrate” or “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

Material 14 might comprise, consist essentially of, or consist ofgermanium, antimony, and tellurium in any mixture or stoichiometry. Atypical and exemplary preferred material is Ge₂Sb₂Te₅.

Referring to FIG. 2, germanium, antimony, and tellurium-comprisingmaterial 14 has been exposed to a plasma-enhanced etching chemistrycomprising Cl₂ and CH₂F₂ effective to etch such material. In thedepicted exemplary FIG. 2 embodiment, only some of material 14 has beenetched. Of course alternately, all of such material might be etched fromover substrate 12 in the depicted exemplary FIG. 2 embodiment, andregardless of whether such plasma-enhanced etching chemistry issubstantially selective to remove material 14 relative to material 12,or whether material 12 would be appreciably etched after the removing ofmaterial 14. In one preferred implementation, the exposing is to aplasma-enhanced etching chemistry consisting essentially of Cl₂ andCH₂F₂ as the only chemically active etching components in the etchingchemistry. Regardless, in one preferred implementation, the exposing isto a plasma-enhanced etching chemistry comprising a molar ratio of from1.5:1 to 1:2 of Cl₂ to CH₂F₂, more preferably from 0.8:1 to 1:1.2, evenmore preferably from 0.9:1 to 1:1.1, even more preferably from 0.95:1 to1:1.15, and most preferably at a molar ratio of 1:1.

In one preferred implementation, the exposing is to a plasma-enhancedetching chemistry comprising inert gas, and in one implementation tosuch a chemistry consisting essentially of Cl₂, CH₂F₂, and inert gas. Byway of example only, exemplary inert gases include N₂ and noble gases. Asingle inert gas might be used, or more than one inert gas might beused. Regardless, the quantity of inert gas in the plasma-enhancedetching chemistry might exceed that of either of the Cl₂ or CH₂F₂ or beless than that of either of the Cl₂ or CH₂F₂. Regardless, when used, thequantity of inert gas in the plasma-enhanced etching chemistry mightexceed that of a sum of the Cl₂ and CH₂F₂ or be less than that of a sumof the Cl₂ and CH₂F₂. In one implementation, the etching occurs within achamber within which plasma is generated. Yet, the invention alsocontemplates remote plasma etching whereby plasma is generated in one ormore etching gases, or mixtures of etching gases, and then fed from achamber within which plasma is generated to a chamber wherein asubstrate is received for plasma-enhanced etching therein, and whereinplasma is not likely generated within the actual deposition chamber.When plasma is generated within the chamber, exemplary reactors include,by way of example only, inductively-coupled reactors andcapacitively-coupled reactors. Regardless, a preferred exemplarytemperature range for the etching is from 10° C. to 80° C., and apreferred pressure range is from 1 mTorr to 80 mTorr. In aninductively-coupled reactor, an exemplary preferred top electrode poweris from 300 Watts to 1200 Watts, and a bottom electrode power of from100 Watts to 800 Watts.

The invention was reduced-to-practice in an Applied Materials DPS PolyEtch system, which is an inductively-coupled reactor. Gas flow to thereactor was 20 sccm Cl₂, 20 sccm CH₂F₂, and 100 sccm of Ar. Substratetemperature was maintained at 25° C., while chamber pressure was kept at10 mTorr. Such produced an etch rate of a layer comprising Ge₂Sb₂Te₅ ofabout 1,400 Angstroms per minute.

The invention was motivated in being able to etch substantiallyvertical/orthogonal sidewalls of a germanium, antimony andtellurium-comprising material or layer, for example as might be utilizedin the fabrication of a memory cell that utilizes resistance variablematerial. By way of example only, additional preferred implementationsof etching material comprising germanium, antimony, and tellurium aredescribed with reference to FIGS. 3 and 4 in combination. Like numeralsfrom the first-described embodiment are utilized where appropriate, withdifferences being indicated with the suffix “a” or with differentnumerals. FIG. 3 depicts a substrate fragment 10 a comprising a suitablesubstrate 12 having a germanium, antimony, and tellurium-comprisingmaterial 14 received thereover. A mask 16 has been formed over material14, and “on” such material, in the depicted preferred embodiment. In thecontext of this document, “on” or “thereon” defines at least some directphysical contacting relationship between the stated materials. Mask 16might comprise one or more different materials and/or regions, andregardless might be entirely sacrificial or some or essentially all ofdepicted mask 16 might remain as part of the finished substrateconstruction. By way of example, one exemplary material for mask 16includes photoresist, including multilayer resist processing which mightinclude one or more hardmasking layers. Further as identified above,mask 16 might comprise multiple layers and/or materials, including oneor more conductive layers which might remain a part of the finishedsubstrate construction.

Referring to FIG. 4, substrate 12/14/16 has been exposed to aplasma-enhanced etching chemistry comprising Cl₂ and CH₂F₂ effective toetch at least germanium, antimony, and tellurium-comprising material 14,as shown. Such is depicted as forming a substantially straight sidewall18 (substantially straight when viewed in a vertical or orthogonalsection view cut as shown) of germanium, antimony, andtellurium-comprising material 14. For purposes of the continuingdiscussion, substrate fragment 10 a can be considered as comprising somesubstrate surface portion 20 over which germanium, antimony, andtellurium-comprising material 14 is received that is proximate depictedsidewall 18. Preferably, the exposing to a plasma-enhanced etchingchemistry comprising Cl₂ and CH₂F₂ forms substantially straight sidewall18 of material 14 which is at an angle that is within 5° of orthogonalto substrate surface 20 on which germanium, antimony, andtellurium-comprising material 14 is received. More preferably, theexposing to such etching chemistry forms sidewall 18 at an angle that iswithin 2° of orthogonal to outer surface 20, and even more preferably atan angle within 1°, and even more preferably is at essentially exactlyorthogonal to such surface as is shown in FIG. 4. Processing andmaterials are preferably otherwise as described above in connection withthe first-described embodiment.

Exemplary implementations, by way of example only, of incorporatingaspects of the above description in methods of forming a variableresistance memory cell are described with reference to FIGS. 5-7. Likenumerals from the above described embodiment have been utilized whereappropriate, with differences being indicated with the suffix “b” orwith different numerals. Referring initially to FIG. 5, and by way ofexample only, an insulative material layer 40 is received over substrate12, and includes a conductive region 42 formed therein. Such mightcomprise a conductive plug and/or line formed within an opening ofmaterial 40, by way of example. Further by way of example only,exemplary materials 40 include silicon nitride and/or doped or undopedsilicon dioxide. An exemplary conductive material 42 includesconductively doped semiconductive materials, elemental metals, alloys ofelemental metals, and/or conductive metal compounds. Material 42 wouldconnect with some other region or conductive device component, and inone exemplary embodiment comprises a conductive inner electrode materialwhich has been formed over a substrate 12. One specific example includesTiN.

A variable resistance chalcogenide material 14 has been formed oversubstrate 12, and comprises germanium, antimony, and tellurium which hasbeen formed over conductive inner electrode material 42, and preferablythereon as shown. A conductive outer electrode material 44 has beenformed over chalcogenide material 14. Such might be of the same ordifferent materials as conductive inner electrode material 42, and ofcourse and regardless, materials 42 and 44 might individually compriseone or more different conductive materials. By way of example only, onepreferred material for conductive outer electrode material 44 includesTiN, and whether material/layer 44 comprises, consists essentially of,or consists of TiN.

A patterned masking material 46 is formed over conductive outerelectrode material 44, and typically/preferably thereon as shown. Anexemplary preferred material 46 comprises photoresist.

Referring to FIG. 6, and using patterned mask 46 as a mask, exemplarymaterial 24 and germanium, antimony, and tellurium-comprising material14 have been plasma etched using a chemistry comprising Cl₂ and CH₂F₂.Exemplary preferred parameters, materials and techniques for such plasmaetching are as described above in the first-described embodiments. Usingthe above exemplary reduction-to-practice example and where material 44consisted essentially of TiN, etch rate of the TiN was at 600 Angstromsper minute.

In the depicted exemplary embodiment, such plasma etching has beeneffective to form substantially straight sidewalls 18 of material 14.For purposes of the continuing discussion, substrate 10 b can beconsidered as comprising respective substrate surfaces 48 on whichgermanium, antimony, and tellurium-comprising material 14 is received.Preferably, substantially straight sidewalls 18 are at an angle within5° of orthogonal to substrate surface 48 proximate sidewalls 18. Morepreferably, such angles are the same as described above in connectionwith the FIGS. 3 and 4 embodiment of substantially straight sidewall 18relative to surface 20.

FIG. 6 depicts the subject etching as forming substantially straightsecond sidewalls 52 of an exemplary TiN-comprising outer electrodematerial 44 which are angled differently relative to outer surface 48 ascompared to the angling of exemplary first sidewalls 18 relative tosurface 48. In one implementation, angles of sidewalls 52 are notorthogonal to surfaces 48, and are at least 5° away from orthogonal tosuch surfaces. In exemplary embodiments, second sidewalls 52 are angledat least 10° away from orthogonal to surfaces 48, and can be angled atleast 20° from orthogonal to surfaces 48, with an exemplary angle of 20°being shown in FIG. 6. FIG. 6 also depicts some lateral dimension lossof mask 46 which might occur and did occur in the abovereduction-to-practice example, but is of course not required.

Referring to FIG. 7, masking material 46 has been removed, leaving anexemplary variable resistance memory cell comprising a conductive innerelectrode material 42, a variable resistance chalcogenide material 44comprising germanium, antimony, and tellurium thereover, and aconductive outer electrode material 44.

An exemplary additional plasma etching chemistry which was utilized anddid not result in the depicted profiles included chemistries in oneinstance having NF₃ as the only chemically active species, and inanother implementation CF₄ as the only chemically active species.Accordingly, most preferably, the preferred plasma etching chemistry isvoid of detectable quantities of either of such gases, although aspectsof the invention do not necessary preclude including one or both gasesin combination with a plasma-enhanced etching chemistry comprising Cl₂and CH₂F₂.

CH₂F₂ has been utilized in gate stacks including one or a combination ofsilicon dioxide, silicon nitride, conductively doped polysilicon, andmetals. However, the chemistries disclosed herein are not understood tohave ever been utilized or suggested for use in etching germanium,antimony, and tellurium-comprising materials.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a variable resistance memory cell, comprising:forming a variable resistance chalcogenide material comprisinggermanium, antimony, and tellurium over a substrate; and plasma etchingthe germanium, antimony, and tellurium-comprising material using achemistry comprising Cl₂ and CH₂F₂.
 2. The method of claim 1 wherein theplasma etching forms a substantially straight sidewall of the germanium,antimony, and tellurium-comprising material which is at an angle that iswithin 5° of orthogonal to a substrate surface proximate the sidewall onwhich the germanium, antimony, and tellurium-comprising material isreceived.
 3. The method of claim 2 wherein the plasma etching forms thesidewall of the germanium, antimony, and tellurium-comprising materialat an angle that is within 2° of orthogonal to said surface.
 4. Themethod of claim 3 wherein the plasma etching forms the sidewall of thegermanium, antimony, and tellurium-comprising material at an angle thatis orthogonal to said surface.
 5. The method of claim 1 comprisingforming the variable resistance chalcogenide material to compriseGe₂Sb₂Te₅.
 6. The method of claim 1 wherein the etching occurs within achamber, plasma being generated within said chamber.
 7. The method ofclaim 1 wherein the etching occurs within a chamber, plasma beinggenerated remote from said chamber.
 8. A method of forming a variableresistance memory cell, comprising: forming a conductive inner electrodematerial over a substrate; forming a variable resistance chalcogenidematerial comprising germanium, antimony, and tellurium over theconductive inner electrode material; forming a conductive outerelectrode material over the chalcogenide material; forming patternedmasking material over the conductive outer electrode material; and usingthe patterned masking material, plasma etching the conductive outerelectrode material and the germanium, antimony, and tellurium-comprisingmaterial using a chemistry comprising Cl₂ and CH₂F₂.
 9. The method ofclaim 8 comprising forming the patterned masking material to comprisephotoresist.
 10. The method of claim 8 comprising conducting said plasmaetching effective to form a substantially straight sidewall of thegermanium, antimony, and tellurium-comprising material which is at anangle that is within 5° of orthogonal to a substrate surface proximatethe sidewall on which the germanium, antimony, and tellurium-comprisingmaterial is received.
 11. The method of claim 8 comprising: conductingsaid plasma etching effective to form a substantially straight firstsidewall of the germanium, antimony, and tellurium-comprising materialwhich is at a first angle that is within 5° of orthogonal to a substratesurface proximate the first sidewall on which the germanium, antimony,and tellurium-comprising material is received; and conducting saidplasma etching effective to form a substantially straight secondsidewall of the conductive outer electrode material which is at a secondangle to said substrate surface that is different from said first angle.12. The method of claim 11 wherein the second angle is not orthogonal tosaid surface, and is at least 5° away from orthogonal to said surface.13. The method of claim 12 wherein the second angle is not orthogonal tosaid surface, and is at least 10° away from orthogonal to said surface.14. The method of claim 13 wherein the second angle is not orthogonal tosaid surface, and is at least 15° away from orthogonal to said surface.15. The method of claim 12 wherein the plasma etching is with a plasmaetching chemistry which is void of detectable NF₃ and CF₄.
 16. Themethod of claim 12 wherein the plasma etching is with a plasma etchingchemistry which comprises at least one NF₃ or CF₄.